Norah Vincent has lived as a man. She didn't undergo a sex change or radical hormone treatments. She simply went undercover. In an extraordinary feat of acting, disguise and guts, Vincent lived among men -- as a man -- for 18 months to see what life was like on the other side of the gender divide.

"This wasn't just a stunt. This was about learning. This is a human project. It was about finding something out about the human creature. ... And I learned it the best possible way because I went through it," Vincent told "20/20's" JuJu Chang.

Growing up in the Midwest with her actress mother, lawyer father and two older brothers, Vincent was a tomboy with a flair for the dramatic. She says she's still a tomboy, and a lesbian living in midtown Manhattan with her partner, Lisa.

At 5 feet, 10 inches and 155 pounds, Vincent passed as a medium-build man she called Ned. Her transformation began with a buzz cut, baggy men's clothes, and a too-small sports bra to flatten her breasts. She even wore a little padding in a jock strap. For the rest, she enlisted the help of makeup artist Ryan McWilliams, who created Ned's five-o'-clock shadow.

Then there was the theatrical component. Vincent underwent months of training with Juilliard voice teacher Kate Maré to learn how to sound like a man. "Women have much stronger nasal resonances as a rule," Maré explained.

When all the pieces were put together -- hair, makeup, voice, posture and style -- the transformation was complete, and Norah Vincent became Ned Vincent.

Becoming One of the Guys

Vincent, a journalist, didn't take the project lightly. She estimates she put on Ned's whiskers and clothes about 150 times during her 18-month experiment. "I wanted to enter males' spheres of interest and ... see how men are with each other. I wanted to make friends with men. I wanted to know how male friendships work from the inside out," she told "20/20."

Vincent's first act as a newly minted male was to join a quintessential bastion of camaraderie -- a men's bowling team in a working-class Pennsylvania neighborhood. The only problem: She's a terrible bowler.

But the men didn't boot her off the team. "It's an amazing thing, because I think that shows you the generosity that they had," she said.

Her experience with these men turned some of her long-held perceptions about men being harsh and rejecting and women being warm and welcoming upside down.

"I mean, it was just the most wonderful rush to get these guys' handshakes, and I felt comfortable, I mean as comfortable as I could feel, right away. They just took me in ... no questions asked," she said.

The team bowled together for nine months and gradually Vincent gained entrance to their inner sanctum. She found that all the cussing and good-natured ribbing is just how men often show affection for one another.

Near the end of the team's run, Vincent decided to reveal herself as a woman. Nervous about how the guys would react, she tested the waters with Jim, the guy she had become closest with.

Vincent took Jim out for a drink with her partner, Lisa, and told him she had something to say that was going to "blow his mind."

"I said the only thing that would blow my mind is if you told me that you were a girl and that she was a guy. And she goes, well, you're half right," Jim said.

Later, Jim told the rest of the teammates, who all took it well.

Jim said he thinks Vincent came into the experiment with some misconceptions about men. "I think she expected to find like a bunch of guys just talking about women's private parts and a bunch of racists and, you know. I think, kind of, that's what she came into this thinking," he said.

Vincent agreed. "They really showed me up as being the one who was really judgmental, because they were the ones who took me in, not knowing anything about me. They were the ones who made me their friend ... no judgments attached," Vincent said.

Sex: 'For a Man, It's an Urge'

Cracking the mystery of a "boys' night out" is one thing, but understanding the explicit world of a man's sexuality is quite another.

To gain an understanding of what some might consider the quintessential male experience, Vincent went to several strip clubs with a male friend. She describes the experience as hellish -- demeaning for the strippers and even worse for the men.

"I saw the men there. I saw the looks on their faces. This is not about appreciation of women, of course. It's not about appreciation of their own sexuality. It's about an urge and ... that's not always that pleasurable, really," she said.

Vincent said strip joints are about pure sex drive -- completely empty of any meaningful interaction, even when a woman is gyrating on your lap.

Even though Vincent is attracted to women, she said she was never aroused during her visits to the clubs. "I really ran smack up against the difference between male and female sexuality. It's that female sexuality is mental. ... For a man, it's an urge," she said.

"At its core, it's a bodily function. It's a necessity. It's such a powerful drive and I think because we [women] don't have testosterone in our systems, we don't understand how hard it is," she said.

Vincent even dabbled in the art of picking up women and agreed to wear a hidden camera for "20/20" during her exploits.

She was quickly reminded that in this arena, it's women who have the power, she said.

"In fact, we sit there and we just with one word, 'no,' will crush someone," she said. "We don't have to do the part where you cross the room and you go up to a stranger that you've never met in the middle of a room full of people and say the first words. And those first words are so hard to say without sounding like a cheeseball or sounding like a jerk."

Vincent encountered some pretty cold shoulders in her attempts at the bar, but she did manage to go on about 30 dates with women as "Ned," mostly arranging them on the Internet.

Vincent said the dates were rarely fun and that the pressure of "Ned" having to prove himself was grueling. She was surprised that many women had no interest in a soft, vulnerable man.

"My prejudice was that the ideal man is a woman in a man's body. And I learned, no, that's really not. There are a lot of women out there who really want a manly man, and they want his stoicism," she said.

Three Weeks at a Monastery

Vincent didn't limit her exploration of masculinity to just friendships and sexuality. She said she found differences in every walk of life, including shopping for a new car at a dealership.

Going in as Norah, the salesman's pitch quickly turns flirtatious, but when she returned to the same salesman as Ned, the tone was all business and the talk was all about the car's performance.

In Vincent's final months as Ned, she managed to infiltrate all-male environments. A lapsed Catholic, Vincent thought it would be interesting to penetrate the cloistered inner world of a monastery. Ned managed to live there for three weeks as a trainee. The monks, Vincent said, were pious, smart men. But they were still men.

She said she witnessed a "desperate need for male intimacy and the lack of ability to give it" at the retreat. It was "really painful," she added.

Not only were the monks struggling to be open and intimate, Vincent said they were hostile to her feminine side. She said she was ostracized because of the monks' assumptions about her sexual orientation.

"Many of them thought I was gay, as one of them told me in confession. ... And I said, 'Well, yeah, but not in the way you think,'" Vincent said.

Vincent thought the perfect end to her 18-month saga would be to join a men-only therapy group, a place where guys tried to bond and show their emotions instead of hiding them.

Again, Vincent saw the men struggle with vulnerability. "They don't get to show the weakness, they don't get to show the affection, especially with each other. And so often all their emotions are shown in rage," she said.

Instead, Vincent said, the men talked about rage, often their rage toward women, and what they would do physically and violently toward women.

"A lot of this was blowing off steam. ...They would talk about fantasizing about chopping up their wives or something. It's not that they would ever do that, but it was a way to get out the blackest thoughts," she said.

Norah began to empathize with the fear and stress men feel for having to always be the strong provider.

Once again, some group members thought Ned was gay, but nobody suspected Ned was a woman. After eight sessions, the group went on a back-country weekend retreat, but Vincent's 18 months of being an imposter was closing in on her.

"The pressure of being someone that you're not and ... the fear of discovery and the deceit that it involves piles up and piles up. So, by the time I got around to doing this men's group, it was really reaching critical mass," she said.

"I was out in the woods with a bunch of guys who had rage issues about women and I was in drag ... and I thought, oh, God, you know, what am I doing," she added.

She continued her emotional descent, and a week later, checked in to a hospital with severe depression. Identity, she concluded, was not something to play around with.

"When you mess around with that, you really mess around with something that you need that helps you to function. And I found out that gender lives in your brain and is something much more than costume. And I really learned that the hard way," she said.

Vincent says she's healed now and glad to be rid of Ned. But her views about men have changed forever.

"Men are suffering. They have different problems than women have, but they don't have it better," she said. "They need our sympathy. They need our love, and maybe they need each other more than anything else. They need to be together."

Ironically, Vincent said, it took experiencing life as a man for her to appreciate being a woman. "I really like being a woman. ... I like it more now because I think it's more of a privilege."